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ACD/Labs Blog

Arvin Moser
The warning flag for this puzzle is evident in the intensities of the signals. For an unknown compound, the TOF-ESI+ mass spectrum below shows the expanded region around four isotope clusters at m/z 300.336 ([M+H]+), 322.307 ([M+Na]+), 599.672 ([2M+H]+) and 621.611 ([2M+Na]+). The intensities of the 13C isotopes (i.e. the [M+1] signal) vary between 40...

Arvin Moser
A key element in data interpretation is to identify any warning flags. Warning flags can help a chemist differentiate good data from bad data. For an unknown compound, the TOF-ESI+ mass spectrum below shows the expanded region around four isotope clusters at m/z 300.336 ([M+H]+), 322.307 ([M+Na]+), 599.672 ([2M+H]+) and 621.611 ([2M+Na]+). Are the intensities...

Arvin Moser
Many analytical data rely on common calculations. This puzzle covers one such common calculation. NMR and MS data were collected on two unknown compounds. The TOF-MS data shows the [M+H]+ at m/z 300.0000 and 600.000 at an error of 0.001 Da. The 500 MHz 1H NMR spectrum shows two chemical shifts at 1500.00 and 3000.00...

Arvin Moser
On the surface, both good data and poor data offer information about an unknown compound. The challenge is to differentiate between what is good data and what is poor data. The purpose of this puzzle is to examine some poor data. From an LC-MS+ TOF dataset, an unknown compound elutes at 2.86 minutes and spans...

Arvin Moser
To identify co-eluting components on a chromatogram, one searches for any distinct differences between the components. There are basically three criteria to check the XICs (extracted ion chromatograms) for to confirm whether the m/z signals pertain to the same component: line shape, signal apex and retention time range. The XICs for m/z 188.1 and 205.1...

Arvin Moser
Sorting out what compounds are present in a mixture is a difficult task. The process is further complicated when the compounds co-elute on a chromatographic run. An LC/MS (ESI+) was collected for an unknown sample comprising of small organic molecules. The total ion chromatogram (TIC shown in black) shows a signal at 2.86 minutes. The...

Arvin Moser
The explanation offered herein covers one possible scenario to a complicated situation. Please note that other explanations are possible. The LC/MS data shows an unknown at 1.8 minutes exhibiting an [M+H]+ at m/z 260 and an [M-H]- at m/z 256. The difference of 4 mass units lends itself into a scenario of conflicting data. One...

Arvin Moser
The purpose of this puzzle is to examine data collected from multiple detectors with the hopes of sorting out the conflicting data surrounding the unknown. In an attempt to identify the structure for an unknown, UPLC data was collected using a C18 column with a run time of 2.2 minutes. The UV, ESI- and ESI+...